fix(clippy): remove unnecessary `to_string()`

tests/formats.rs

@@ -176,12 +176,8 @@ fn test_format_generation(texname: &str, fmtname: &str, sha256: &str) {
             let observed = info.write_digest.unwrap();
 
             if observed != want_digest {
-                println!(
-                    "expected {} to have SHA256 = {}",
-                    fmtname,
-                    want_digest.to_string()
-                );
-                println!("instead, got {}", observed.to_string());
+                println!("expected {} to have SHA256 = {}", fmtname, want_digest);
+                println!("instead, got {}", observed);
                 panic!();
             }
         }